In recent years, it has turned out to be effective, for healing a wound, not to dry the wound surface but to keep it in a moist environment. In particular, since an ingredient contained in the exudate from a wound site is useful to promote the healing of a wound, a method in which a wound is not disinfected but treated in a moist environment created by the exudate from the wound site (hereafter may be called “moist healing”) has turned out to be effective. Therefore, various kinds of wound dressings applicable to such a therapeutic method have been developed.
In order to perform a moist healing effectively, it is important that a moderate moist environment is maintained at a wound surface by the exudate from a wound site. Therefore, it is needed that a wound dressing has a function of moderately holding exudate on a wound surface instead of rapidly absorbing it. However, the moist healing allows a closed area to be formed on the wound surface since a wound dressing is firmly fixed to the skin in order to maintain a moist environment. As a result, when additional exudate oozes and is superfluously retained, the wound surface is compressed by exudate, leading to an “undermining” (a phenomenon in which the skin is hollowed by the pressure of exudate at a wound site). For this reason, it is also needed that the wound dressing has a function of moderately discharging exudate from on the wound surface.
In addition, if the material in contact with a wound site does not have breathability and sticks tight to the wound surface, removing the wound dressing can damage the healed or healing wound again. Therefore, it is also needed that the wound dressing does not stick tight to a wound surface.
As a conventional wound dressing, for example, JP-A-7-80020 discloses a dressing utilizing a porous film containing a dispersed hydrophilic substance or being coated with a hydrophilic substance. However, in this wound dressing, only the exudate-discharging function is improved by utilizing a hydrophilic porous film, and the objective of moderately holding exudate on a wound surface is not achieved.
Also, JP-A-10-151184 discloses a wound dressing applied onto an ulcer surface, which is formed of cotton, knitted or woven fabric, nonwoven, etc. containing chitin-chitosan cellulose mixed fibers, with a hydrocolloid agent applied thereto if desired. However, in the wound dressing, emphasis is placed on the function to absorb exudate, and the function to moderately hold exudate on a wound surface is insufficient. Further, it has been pointed out that a prolonged direct contact of the skin with the hydrocolloid agent of the wound dressing will cause a skin redness or a heat rash.
In order to solve the problems of conventional wound dressings set forth above, the inventor has developed a wound dressing having a sheet material that exerts an initial water pressure resistance as a permeable layer in contact with a wound site, and already applied for an international patent on it (see WO 2005/000372). The wound dressing has outstanding functions for use in a method to treat a wound while maintaining a moist environment created by the exudate from the wound site.